We propose to study the effect of various levels of lung inflation on pulmonary blood volume and pulmonary extravascular water, under conditions of low vascular pressure and hemodynamic edema. We have chosen to work with a perfused isolated canine lobe preparation which will allow us to observe the effect of a change in transpulmonary pressure alone on pulmonary blood volume and pulmonary extravascular water under controlled vascular pressures and flows. Morphologic studies will parallel physiologic measurements in the attempt to clarify the distribution of extravasated fluid during the early phase of interstitial pulmonary edema. We will investigate the effect of accumulation of fluid around small airways on their tendency to collapse at low transpulmonary pressure and will determine whether "closing volume" is present in an isolated pulmonary lobe and how it is affected by interstitial edema. The outlined work should lead to a more rational approach to assisted ventilation in the treatment of pulmonary edema in the clinical setting.